Gear Ratio Explorer

Definition

Gear ratio = driven teeth / driver teeth. It describes how many times the driven gear turns for every one revolution of the driver gear.

Reading the ratio

A 2:1 ratio means the driven gear completes one full turn for every two turns of the driver. A 1:2 ratio means the driven gear spins twice for each driver revolution.

Direction of rotation

Two external gears meshing directly always rotate in opposite directions. The driver turns clockwise while the driven gear turns counterclockwise.

The fundamental rule

Gears cannot create energy. When you gain speed you lose torque, and when you gain torque you lose speed, always in exact proportion (assuming no friction).

Torque increase (reduction gearbox)

Small driver, large driven gear. The driven gear turns slower but with proportionally more torque. Used in electric motors driving heavy loads, lug wrenches, and drill presses.

Speed increase (overdrive)

Large driver, small driven gear. The driven gear spins faster but produces less torque. Used in bicycle chain rings, lathe headstocks, and clock escapements.

What it measures

Mechanical advantage (MA) is the ratio of output force to input force. For a simple gear pair MA equals the gear ratio: MA = driven teeth / driver teeth.

MA greater than 1

The output delivers more torque than the input. The machine multiplies force at the cost of speed. Useful when you need to move heavy loads with a smaller motor.

MA less than 1

Output torque is less than input torque, but output speed exceeds input speed. Useful in applications requiring high rotational speed such as cooling fans or generators.

Ideal vs real

This tool shows ideal mechanical advantage. Real gears lose energy to friction, so actual output torque is always slightly less than the theoretical maximum.

Bicycle gears

Derailleur systems move the chain between different-sized sprockets to change the gear ratio. A large front ring with a small rear cog gives high speed (flat road); a small front ring with a large rear cog gives low speed but high torque (steep hill).

Car transmissions

Lower gears use large driven sprockets (high gear ratio) to maximize torque for acceleration. Higher gears use near-1:1 ratios for efficient highway cruising.

Analog clocks

Gear trains convert the fast oscillation of the escapement wheel into the slow, precise rotation of the hour hand. A series of gear pairs multiply speed reductions through the gear train.

Industrial gearboxes

Electric motors spin at 1200-3600 RPM. Gearboxes reduce this to the 10-100 RPM needed by conveyors, mixers, and pumps while multiplying torque by the same factor.